Facile and scalable bilayer polymer encapsulation to achieve long-term stability of perovskite solar cells under harsh humidity conditions

Abstract

Perovskite solar cell (PSC) technology has shown remarkable progress in the domains of power conversion efficiency (PCE) and cost-effective fabrication process but its poor environmental stability is a serious issue that is foiling upscaling and extensive outdoor applications. PSCs are prone to undergo rapid degradation when subjected to humid environments which results in low device lifetimes. To prevent the degradation caused by the infiltration of moisture and oxygen into the perovskite absorber layer, a suitable encapsulation layer is paramount. Keeping this in mind, in this study a facile, scalable and solution-based bilayer encapsulation strategy was used to protect the PSCs. The bilayer encapsulation stack comprises a relatively hydrophilic poly(methyl methacrylate) (PMMA) and a hydrophobic polyurethane (PU) polymer layer. The encapsulation materials and strategy did not damage the perovskite absorber layer and other organic layers present in the device stack. The bilayer (PMMA/PU) encapsulated perovskite absorber films show no degradation or phase change even after ∼28 days (670 h) when stored under harsh relative humidity conditions (80 ± 5% RH). In addition, the PMMA/PU encapsulated devices retained more than 92% of their initial power conversion efficiency (PCE) after 1500 h (∼60 days) under these conditions (80 ± 5% RH). On the other hand, the unencapsulated devices showed severe and rapid degradation in 48 h. Thus, this study introduces a simple solution processable bilayer encapsulation method, which holds promise for potential application not only in the area of flexible perovskite solar cells and modules but also in various other optoelectronic devices such as organic solar cells and light-emitting devices.